Currently, research and development for a satellite mobile communication system using a complementary terrestrial component (CTC), such as a repeater, a complementary ground component (CGC), and an ancillary terrestrial component (ATC), has been actively progressed worldwide.
In case of Korea, a satellite digital multimedia broadcasting (DMB) system currently provides services. On the other hand, in case of Europe, research into a digital video broadcasting—satellite services to handhelds (DVB-SH) system has been actively progressed for providing broadcasting services by 2010. A subsidiary of SkyTerra Communications, Inc. in U.S.A. Mobile Satellite Ventures and Terrestar™ have developed a terrestrial satellite integrated system for providing audio and data communications using an ATC at the downtown area and the suburbs.
First, a satellite DMB system in Korea is designed to allow a receiver for a vehicle or a fixed or portable receiver to receive high-quality audio signals and multimedia signals by auxiliarily using a terrestrial network using a co-channel gap filler together with a satellite. The satellite and terrestrial systems are optimized in a band of 2630 to 2655 MHz. The system is configured to include a feeder link earth station and a broadcasting satellite, two types of terrestrial repeaters, and a receiver (vehicle, fixed, portable).
First, transmission signals are transmitted to a satellite through the feeder link earth station. In this case, an uplink line uses a band (ex, 14 GHz) for a fixed satellite service (FSS). The received signals are converted into a 2.6 GHz band in the satellite and amplified at a desired size using an amplifier in a satellite repeater, which are in turn broadcast to service areas.
A user of the system may receive signals using a small antenna having low directivity. To this end, the small antenna needs to have a sufficient magnitude of equivalent isotropic radiated power (EIRP). For this reason, a satellite vehicle needs to have a large-sized transmitting antenna and a high output repeater. An example of main problems caused at the time of propagating signals of 2.6 GHz band may include shadows and obstacles on a direct path from a satellite. In order to overcome the above problems, a repeater of retransmitting satellite signals is added in a system design.
The repeater supplements portions that are covered by obstacles such as buildings. The repeater is divided into a direct amplification repeater and a frequency conversion repeater.
The direct amplification repeater is designed in a type which simply amplifies broadcasting signals of 2.6 GHz received from a satellite and is essentially designed in a type of a low gain amplifier so as to avoid unnecessary divergence due to signal interference generated between receiving and transmitting antennas. The direct amplification repeater covers a narrow area up to 500 m based on a line of sight (LOS).
On the other hand, the frequency conversion repeater covers a wide area up to 3 Km and converts and transmits the received signals of 2.6 GHz band into another frequency band (for example, 11 GHz). In the environment, multi-path fading that receives at least two signals occurs. The system uses a rake receiver that uses a code division multiplexing (CDM) technology so as to stably receive multi-path fading signals.
The DVB-SH system in Europe is a system that uses a satellite in nationwide coverage and uses CGC in indoor environment and terrestrial coverage. The DBV-SH system in Europe aims to provide DVB-H based mobile TV services at 15 MHz bandwidth of S band. Since the DBV-SH system uses a band approximating a band for international mobile telecommunication (IMT) of S band, the integration with the IMT terrestrial part is easily performed and the network reuse with a terrestrial network is easily performed, thereby reducing installation costs. The DBV-SH system considers a hybrid broadcasting structure with a terrestrial network and considers a structure in which a reuse factor for a CGC cell in a single satellite spot beam is set to be 1 and a reuse factor for a satellite spot beam is set to be 3 so as to effectively use a frequency while solving a signal interference problem between the satellite and the CGC. In this case, France may broadcast 9 TV channels for nationwide coverage through the satellite spot beam and 27 TV channels using a terrestrial repeater in the downtown area or the indoor environment.
Finally, MSV and Terrestar in U.S.A. have developed a geostationary satellite based satellite mobile communication system to provide ubiquitous wireless wide area communication services such as internet connection, voice call, or the like, in an L band and an S band to user equipments such as a personal communication system (PCS) or a cellular phone. The system uses a hybrid wireless network structure in which a satellite is coupled with the ATC, wherein the hybrid wireless network structure is to provide audio or high-speed packet services through the ATC, that is, the terrestrial network in the downtown area or the densely populated area in U.S.A. and Canada and services through a satellite in the country or the suburbs that are not covered by the ATC. The ATC mainly uses a radio interface such as a satellite so as to provide satellite services without almost increasing complexity of a terrestrial user equipment.
On the other hand, when considering only the satellite service without considering commonality with the terrestrial network like a Thuraya system, the satellite mobile system uses the radio interface optimized for the satellite environment like a GMR radio interface, thereby reducing an overhead of a satellite payload and implementing a system optimized for the satellite mobile environment.
However, in the Thuraya system, the user equipment needs to have a dual chip embedded therein for supporting the satellite and terrestrial radio interface so as to use both of the satellite and the terrestrial services,
Consequently, the satellite mobile system developed up to now selects one of the commonality with the terrestrial network and the optimization of the satellite environment to use the radio interface so as to be matched with the situations.
However, when the satellite mobile system and the satellite radio interface that are currently developed select one direction to start the satellite mobile service, switching to another direction means the replacement of the entire system in the currently developed system situations, which cannot be realized.